Jesse James Garrett gives a name to "Asynchronous JavaScript + XML" and says it represents a fundamental shift in what’s possible on the Web.
The biggest challenges in creating Ajax applications are not technical. The core Ajax technologies are mature, stable, and well understood. Instead, the challenges are for the designers of these applications: to forget what we think we know about the limitations of the Web, and begin to imagine a wider, richer range of possibilities.
It’s going to be fun.